The Cenozoic history of New Zealand températe rainforests: comparisons with southern Australia and South America

Abstract

The temperate rainforests of southern hemisphere continents share Gondwanan antecedents, but subsequent trajectories exhibit divergent patterns. We review the Cenozoic history of major forest elements (c. 30 genera/families) of the temperate rainforests of New Zealand and compare these with South America and southeast Australia. From macro- and microfossil evidence, the major structural components of temperate rainforests in New Zealand have lineages dating back almost continuously to the Eocene or earlier. These include the tree ferns (Cyathea and Dicksonia), Agathis, all but one of the podocarps, Nothofagaceae and other broadleaved genera such as Lauraceae and Cunoniaceae. Collectively these taxa contribute approximately 50% of current biomass in New Zealand temperate forests. However, several previously important groups in the Cenozoic such as Araucaria, the Brassospora-type beeches, and Casuarinaceae became extinct in New Zealand in the Miocene to Pleistocene. Patterns of extinction are broadly similar in New Zealand and South America (mostly late Miocene to Pleistocene) in response to climate cooling along steepened environmental gradients whereas in southern Australia taxa became extinct later (Pleistocene) reflecting limited suitable habitat during glacials. The deep-time continuity evident in the composition of New Zealand temperate rainforests was not influenced by the decrease in land area during the maximum marine transgression in the late Oligocene (c. 25–24 million years ago). Forest canopy dominants and emergents appear to have remained remarkably stable, perhaps reflecting community resilience. However, new subcanopy and open habitat lineages arrived as forest taxa were extirpated and climates cooled, reducing potential forest habitats.